the serial console speed (i386 and amd64 only). If the previous
stage boot loader requested a serial console (RB_SERIAL or RB_MULTIPLE)
then the default speed is determined from the current serial port
speed. Otherwise it is set to 9600 or the value of BOOT_COMCONSOLE_SPEED
at compile time.
This makes it possible to set the serial port speed once in
/boot.config and the setting will propagate to boot2, loader and
the kernel serial console.